Display device

ABSTRACT

The invention relates to a display device, especially in a motor vehicle, comprising a display ( 2 ) which can be illuminated by a light source ( 1 ), and a light guide ( 7 ) which is arranged between the light source ( 1 ) and the display ( 2 ). Said light source ( 1 ) comprises a plurality of individual light sources ( 10 ), the entire light-radiating surface of said light sources being larger than the surface of the display ( 2 ). In order to increase the light efficiency, the light guide ( 7 ) comprises, on the light source side, individual light guiding sections ( 12 ) which are associated with the individual light sources ( 10 ), said sections forming a common light guiding section ( 13 ) on the display side.

[0001] The invention relates to a display device, in particular in amotor vehicle, having a display that can be illuminated by a lightsource, and a light guide arranged between the light source and display,the light source having several individual light sources whose overalllight-emitting surface is larger than the surface of the display.

[0002] Such display devices are known, and are used, for example inmotor vehicles for instrument illumination. By contrast with displaysthat can be illuminated by intense individual light sources such as, forexample, halogen lamps or fluorescent lamps, these devices can have alower power consumption and reduced heat loss emission.

[0003] For reasons of traffic safety, there is an urgent need in motorvehicles for the individual display instruments to have a brightnessthat enables them to be read even given high ambient brightness. This isalso of great importance, in particular, for so-called headup displayswhere—as described in DE 198 52 842 C1, for example—an image isreflected into a front pane of the motor vehicle. Because of theconstricted space conditions generally applying in the region of thedashboard of the motor vehicle in which the display device is fitted,and of the therefore problematic use of intense light sources that,firstly, require a large installation space and, secondly, emit asubstantial heat loss, an attempt is being made to replace theindividual light source by a plurality of light sources that admittedlyeach have a low light intensity per se, but which also have a low heatloss emission. The problem arises in this case that because of geometricboundary conditions—the miniaturization of these light sources islimited—the arrangement of light sources requires a larger surface thanthat to be illuminated.

[0004] A known solution to this problem consists in arranging betweenthe light sources and display a light guide in the form of a solidpyramidal frustum whose base surface adjoins the light sources and whichtapers in the direction of the display. Owing to this shape of the lightguide, the light beams emerge from the light guide at a larger anglethan that at which they entered it. This opposes the requirement for anarrow light emission angle that ensures a high intensity ofillumination. Again, there are disadvantageous light losses owing to theexit of light at the side surfaces of the light guide, since the lightbeams impinge on the surface on each reflection at a relatively largeangle near the perpendicular, and the total reflection is therebycancelled.

[0005] It is therefore the object of the invention to configure adisplay device of the type mentioned at the beginning such that thelight emitted by the individual light sources is available forilluminating the display in a way as free as possible from losses.

[0006] This object is achieved according to the invention by virtue ofthe fact that either the light guide has individual light guidingsections that are assigned to the individual light sources on the lightsource side and which merge on the display side into a common lightguiding section, or in that the light guide has convex lens elements onits light entrance side facing the light source and on its light exitside facing the display, the individual light sources respectively beingassigned a convex lens element, corresponding to a convex lens elementon the light exit side, on the light entrance side. Light losses cantherefore be avoided as far as possible in a simple way. In the case ofthe second solution, the light is guided between the convex lenselements on the light entrance side and those on the light exit side ofthe light guide the light is in a fashion focussed by thefirst-mentioned lens elements and avoiding scattering losses. Thedisplay device according to the invention also has a very low spacerequirement and permits the use of any desired light sources. The powerefficiency of the device is very high, and there is no need for anadditional cooling device even in the case of a restricted installationin the dashboard of a motor vehicle.

[0007] A further increase in the light efficiency is achieved with theaid of an advantageous development of the display device according tothe invention, in which the emission angle of the light emerging fromthe light guide is exactly equal to or less than the emission angle ofthe light radiated by the light source. In this way, the light is notonly led with low losses in the light guide from the light source to thedisplay, but is focussed in addition at the same time in a fashion thatincreases intensity.

[0008] Any desired arrangement of the individual light sources isconceivable owing to the possibility of freely configuring and arrangingthe individual light guiding sections. Particularly in the case ofapproximately rectangular displays, however, it is of particularadvantage when the individual light sources are arranged in matrix form.This gives rise to particularly short light guiding paths which are, inaddition, largely free of light losses, since the light paths have noadditional deflections or diversions.

[0009] In accordance with another advantageous development of theinvention, the individual light sources are LEDs, and this is attendedby an increased service life of the illumination unit and by an onlyslight incidence of heat loss.

[0010] The display device according to the invention can be producedparticularly easily and also in very large numbers such as occur formotor vehicle applications, in particular, when the individual lightsources are preferably arranged on a printed circuit board and makeelectric contact with the latter. In addition, individual electricconnections to be fitted expensively are thereby rendered superfluous.It is particularly advantageous in this case when the printed circuitboard has a high thermal conductivity such that the risk of overheatingof the light sources can be excluded even given high ambienttemperatures.

[0011] Particularly in the case of a very restricted installation of thedisplay device according to the invention in an environment that iswarm, in addition, it is advantageous in accordance with a furtherdevelopment when the light source has a cooling element for dissipatingheat from the individual light sources.

[0012] In accordance with a further advantageous development of theinvention, the light source has convex lenses on its light exit sidefacing the light guide, a convex lens corresponding in each case on theone hand to an individual light source and on the other hand to anindividual light guiding section. Focussing of the light, and thus aneven further-reaching optimization of the light efficiency is therebyachieved.

[0013] In this case, both the production, for example using aninjection-molding method, and the mounting of the convex lenses areparticularly simple, when the convex lenses are advantageously connectedto one another in a fashion forming a single convex lens component. Aneven further-reaching design simplification and reduction in the numberof components result in accordance with a further advantageousdevelopment of the invention when in each case a convex lens isconnected to an individual light source in a fashion forming a singlecomponent. This can be achieved, for example, by virtue of the fact thatthe convex lenses are molded onto the individual light sources in eachcase using an injection-molding method, or that they are mounted inanother way, for example by being cast with epoxy resin.

[0014] Arbitrarily transilluminable images could be envisaged as thedisplay. However, it is particularly advantageous when the display has atransilluminable LCD, particularly for a variable representation ofinformation in a compact display device that can also be produced inlarge numbers cost-effectively and has a long storage life.

[0015] In accordance with a further advantageous development of theinvention, a particularly lightweight, cost-effective light guide ofhigh efficiency is achieved when the light guide consists of atransparent, light-guiding plastic. PMMA (polymethyl methacrylate) hasproved to be a material outstandingly suited to this purpose. With thismaterial, the light guide has very good optical properties.

[0016] Light is guided with particularly low losses in the case of thefirst solution when, in accordance with a further advantageousdevelopment of the invention, the individual light guiding sections aredesigned as fingers with an approximately constant cross-sectional area.

[0017] Moreover, the light efficiency can be further improved when, inaccordance with a further advantageous development of the invention, inthe first embodiment the individual light guiding sections have a convexlens on their light entrance side facing the light source.

[0018] On the light exit side of the light guide, the focussing of thelight, and thus also the light efficiency are advantageouslyadditionally improved when, in the first solution, the light guide isconvex overall at its light exit side facing the display. Instead of theone convex shape, the light guide can advantageously have convex lenselements on its light exit side facing the display, the convex lenselements respectively being assigned to a light guiding section. Aparticularly good tuning of the light guiding sections and convex lenselements can thereby be achieved.

[0019] In the case of the second solution, it can be envisaged, forexample, to provide in the light guide directional and/or deflectingelements with the aid of which the light is guided from the entranceside of the light guide to its exit side. A particularly lightweightlight guide for which only a small amount of material is required inconjunction with very low loss light guidance prevails advantageously,by contrast, when a first central connecting straight line, between afirst convex lens element on the light exit side and a first convex lenselement, corresponding thereto, on the light entrance side, and a secondcentral connecting straight line, between a second convex lens elementon the light exit side and a second convex lens element, correspondingthereto, on the light entrance side of the light guide are arranged atan angle to one another.

[0020] In this case, the outlay on material for the light guide can befurther reduced, and accumulations of material that can lead toinhomogeneities are avoided when, in accordance with an advantageousdevelopment of the invention, a region of space, arranged between thefirst and second connecting straight lines, of the light guide iscleared of material in a fashion forming an interspace.

[0021] The display device can basically have any desired displays.However, in accordance with a further advantageous development of theinvention it is particularly advantageous when it comprises a headupdisplay in a motor vehicle, since the advantages of high lightefficiency, small installation space and low heat emission therebyespecially come to bear.

[0022] The invention is explained in more detail below with the aid ofexemplary embodiments illustrated in the attached drawing in which:

[0023]FIG. 1 shows an illustration of the principle of a headup displayin a display device in a motor vehicle,

[0024]FIG. 2a shows a detail of a display device in a sectional sideview,

[0025]FIG. 2b shows an alternative light source of a display deviceaccording to FIG. 2a,

[0026]FIG. 3 shows a detail of the illustration according to FIG. 2a ina sectional, perspective view,

[0027]FIG. 4 shows a light guide of another display device,

[0028]FIG. 5 shows a light guide of a further display device,

[0029]FIG. 6a shows a detail of a display device in a sectional sideview in a second embodiment,

[0030]FIG. 6b shows an alternative light source of the display deviceaccording to FIG. 6a, and

[0031]FIG. 7 shows a detail of a light source in a sectional,perspective view.

[0032] Respectively corresponding elements are provided with identicalreference numerals in the figures.

[0033] A headup display 16 is shown in FIG. 1 in a schematic displaydevice 40 of a motor vehicle (not illustrated here in more detail). Animage produced with the aid of a display 2 that can be illuminated by alight source 1 with the aid of a light guide 7, 57, is reflected,following the beam path 15 depicted, at a deflecting mirror 3 and ledvia a concave mirror 4 to a windshield 5 from where the image is passedon as a virtual image into an eye, marked by an eye position 6, of aviewer (not further illustrated), for example the motor vehicle driver.

[0034] The particulars of a detail of a display device in a firstembodiment are shown in FIG. 2a. It is to be seen here that a display 2formed by an LCD can be illuminated by a light source 1 via aninjection-molded light guide 7 made from transparent, light-guidingplastic. The light source 1 has a printed circuit board 9 on the frontside of which, facing the light guide 7, a number of individual lightsources 10 are arranged and fastened and make electric contact. Theindividual light sources 10 are formed by LEDs, and the overalllight-emitting surface of the individual light sources 10 is greaterthan the surface of the display 2. On its rear side, the printed circuitboard 9 is provided with a cooling element 8, having cooling ribs 19,for dissipating the heat produced by the light sources 10.

[0035] The light guide 7 has individual light guiding sections 12constructed as fingers with a cross-sectional surface 28, 28′ that isapproximately constant in their course, one of the individual lightsources 10 being assigned in each case to a beginning 20 of anindividual light guiding section 12. Moreover, for the purpose offocussing the light emitted in each case by the individual light sources10, the light source 1 is provided with a convex lens component 11 thathas a plurality of convex lenses 14 that are connected to one another ina fashion forming a single component. The arrangement is selected insuch a way that in each case a convex lens 14 is arranged upstream of anindividual light source 10 such that the light radiated by in each caseone individual light source 10 is focussed in a defined and targetedfashion by an assigned convex lens 14 in each case. It is also to beseen that the individual light guiding sections 12 merge into a commonlight guiding section 13 at their end 21 facing the display. As a resultof this, the light of the individual light sources 10 is mixed, with theresult that a uniformly, evenly illuminated surface is produced on theside of the light guide 7 where the light is coupled out.

[0036] An alternative light source 1 with a cooling element 8 havingcooling ribs 19 is shown in FIG. 2b. With this light source 1, as well,individual light sources 10 constructed as LEDs are arranged on aprinted circuit board 9 and brought into electric contact with thelatter. By contrast with the light source according to FIG. 2a, thelight source 1 according to FIG. 2b does not, however, have a convexlens component with a plurality of convex lenses, but in each case aconvex lens 30 is connected to an individual light source 10 in afashion forming a single component. For this purpose, the convex lenses30 consist of plastic and are, for example, molded in each case onto oneof the individual light sources 10 using an injection-molding method.

[0037] In order to explain the spatial design of the light source, FIG.3 illustrates in a sectioned perspective view the printed circuit board9 with individual light sources 10 arranged thereon, and with theassigned convex lens component 11 having the convex lenses 14.

[0038] The individual light sources 10 formed by LEDs are arranged inmatrix form 26, and they are assigned in each case a convex lens 14 ofthe convex lens component 11.

[0039]FIG. 4 shows a further light guide 7. It is to be seen here, too,that individual light guiding sections 12 are constructed as fingerswith a cross-sectional surface 28, 28′ that remains approximatelyconstant in their course. Moreover, in this embodiment the individuallight guiding sections 12 in each case have a convex lens 17—illustratedin a stylized fashion—on their light entrance side 22 facing the lightsource (not illustrated here). Moreover, the light guide 7 has on itslight exit side 23 facing the display—likewise not illustratedhere—convex lens elements 18 that are respectively assigned to anindividual light guiding section 12 and are located on a common lightguiding section 13.

[0040] The embodiment according to FIG. 5 differs from that according toFIG. 4 in that rather than individual convex lens elements beingarranged on the light exit side 25, facing the display, of a light guide7, the light guide 7 itself is convex overall, specifically in a commonlight guiding section 29 that combines individual light guiding sections12. The light exit side 25, arranged on the common light guiding section29, of the light guide 7 is consequently curved like a barrel. Theindividual light guiding sections 12 of the light guide 7 are providedat their light entrance side 24 with convex lens elements 18—illustratedin a stylized fashion.

[0041] Particulars of a detail of a display device in the secondembodiment are shown in FIG. 6a. Here, a display 2 formed by atransilluminable LCD can be illuminated by a light source 1 via a lightguide 57 made from transparent, light-guiding plastic. The light source1 has a printed circuit board 59 on the front side of which, facing thelight guide 57, a number of individual light sources 60 are arranged andfastened and make electric contact. The individual light sources 60 areformed by LEDs, and the overall light-emitting surface of the individuallight sources 60 is greater than the surface of the display 2. On itsrear side, the printed circuit board 59 is provided with a coolingelement 58, having cooling ribs 70, for dissipating the heat produced bythe light sources 60. Moreover, the printed circuit board 9 itself has ahigh thermal conductivity, and thus contributes to the dissipation ofheat.

[0042] The light guide 57 has convex lens elements 61 on its lightentrance side 71 facing the light source 1, in each case one of theconvex lens elements 61 corresponding to one of the individual lightsources 60. Each individual light source 60 radiates light essentiallyinto in each case one convex lens element 61 that focuses the lightemitted by the individual light source 60.

[0043] The arrangement is selected here in such a way that in each casea convex lens 61 is arranged upstream of an individual light source 60in such a way that the light radiated by in each case one individuallight source 60 is focussed in a defined and targeted fashion by in eachcase one assigned convex lens 61. Further convex lens elements 62 arearranged on the light exit side 72, facing the display 2, of the lightguide 57. In each case one of the convex lens elements 61 on the lightentrance side 71 of the light guide 57 is assigned a convex lens element72 on the light exit side 72 of the light guide 57.

[0044] The basic shape of the light guide 57 is approximately that of awedge, this being seen in the fact that a first connecting straight line68, which runs through a first convex lens element 62′ on the light exitside 72 and through a first convex lens element 61′, correspondingthereto, on the light entrance side 71, and a second connecting straightline 69, which runs through a second convex lens element 62″ on thelight exit side 72 and through a second convex lens element 61″corresponding thereto, on the light entrance side 71, are arranged at anacute angle α to one another. Both the first connecting straight line 88and the second connecting straight line 69 are arranged centrally inrelation to the convex lens elements 61′, 62′, 61″, 62″ intersected bythem.

[0045] Furthermore, a region of space 67, arranged between the firstconnecting straight line 68 and the second connecting straight line 69,of the light guide 57 is cleared of material in a fashion forming aninterspace. The region of space 67 contributes essentially nothing tothe guiding of the light from the light source 1 to the display 2; thefact that it is freed from material firstly reduces the weight of thelight guide 57, and secondly avoids accumulation of material possiblyleading to inhomogeneities.

[0046]FIG. 6b shows an alternative light source 1 with a cooling element58 having cooling ribs 70, and a detail of a light guide 57. In the caseof this light source 1, as well, individual light sources 60 designed asLEDs are arranged on a printed circuit board 59 and brought intoelectric contact therewith. By contrast with the light source accordingto FIG. 6a, the individual light sources 60 of the light source 1according to FIG. 6b in each case have a convex lens 74, each individuallight source 60 being connected to the convex lens 74 assigned to it ina fashion forming a single component. For this purpose, the convexlenses 74 are made from plastic and are molded onto the individual lightsources 60 in each case using an injection-molding method. The convexlenses 24 serve in each case to focus the light radiated by anindividual light source 60 in a defined and targeted fashion.Furthermore, in each case a convex lens 74 corresponds to a convex lenselement 61 on the light entrance side 71 of the light guide 57, theconvex lenses 74 and the convex lens elements 61 being arranged oppositeone another in each case.

[0047] In order to explain the spatial design of a further light source,FIG. 7 illustrates in a sectioned perspective view the printed circuitboard 59 with individual light sources 60 arranged thereon, and with anassigned convex lens component 64 having convex lenses 63. Theindividual light sources 60 formed by LEDs are arranged in matrix form73, and they are assigned in each case a convex lens 63 of the convexlens component 64. The arrangement is selected here in such a way thatin each case a convex lens 63 is arranged upstream of an individuallight source 60 such that the light radiated by in each case oneindividual light source 60 is focussed in a defined and targeted fashionby in each case one assigned convex lens 63.

1.-20. (canceled)
 21. A display device for a motor vehicle, comprising: a display having a display surface; a light source having a plurality of individual light source elements for illuminating said display, said light source having an overall light-emitting surface that is larger than said display surface of said display; and a light guide arranged between said light source and said display and having a light source side facing said light source and a display side facing said display, said light guide having one of individual light guiding sections on said light source side which merge into a common light guiding section on said display side, or convex lens elements on said light source side and said display side, wherein each of said plural light source elements is assigned to one of said convex lens elements on said light source side and a corresponding convex lens element on said display side.
 22. The display device of claim 21, wherein an emission angle of the light emerging from the light guide is equal to or less than an emission angle of the light radiated by said light source.
 23. The display device of claim 21, wherein said individual light source elements are arranged in a matrix.
 24. The display device of claim 21, wherein said individual light source elements comprise LEDs.
 25. The display device of claim 21, wherein said light source comprises a printed circuit board, said individual light source elements being arranged on said printed circuit board for making electrical contact with said printed circuit board.
 26. The display device of claim 25, wherein said printed circuit board has a high thermal conductivity.
 27. The display device of claim 21, wherein said light source comprises a cooling element for dissipating heat from said individual light source elements.
 28. The display device of claim 21, wherein said light guide comprises said individual light guide sections and said light source comprises convex lenses on a side facing said light guide, each of said convex lenses corresponding to one of said individual light source elements and to one of said individual light guiding sections on said light source side of said light guide.
 29. The display device of claim 28, wherein said convex lenses are interconnected with one another for forming a single convex lens component.
 30. The display device of claim 28, wherein each of said convex lenses is connected to one of said individual light source elements forming a single component with said one of said individual light sources.
 31. The display device of claim 21, wherein said display comprises a transluminable LCD.
 32. The display device of claim 21, wherein said light guide is made of a transparent, light guiding plastic.
 33. The display device of claim 32, wherein said plastic is polymethyl methacrylate (PMMA).
 34. The display device of claim 33, wherein said light guide comprises said individual light guiding sections extending from said display side to said light source side and having an approximately constant cross-sectional area.
 35. The display device of claim 34, wherein said light guide comprises said individual light guiding sections, wherein each of said individual light guiding sections comprises a convex lens on said light source side of said light guide.
 36. The display device of claim 21, wherein display side of said light guide is a convex surface.
 37. The display device of claim 21, wherein said light guide comprises said individual light guiding sections and includes convex lens elements on said display side, said convex lens elements respectively being assigned to said individual light guiding sections.
 38. The display device of claim 21, wherein a first central connecting straight line between a first one of said convex lens elements at said display side and a corresponding first one of said convex lens elements at said light source side, and a second central connecting straight line between a second one of said convex lens elements on said display side and a corresponding second one of said convex lens elements on said light source side of said light guide are arranged at an acute angle (α) to one another.
 39. The display device of claim 38, a space arranged between said first and second connecting straight lines of said light guide is cleared of material thereby forming interspace.
 40. The display device of claim 21, wherein said display device comprises a headup display in a motor vehicle. 